Near Infrared Nanoparticles Shine A Bright Light On Cancer

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Their research, utilizing encapsulated fluorescent molecules incalcium phosphate nanoparticles and non-toxic near infrared imaging(NIR), appears in the Sept. 19 on-line issue of ACS Nano.
More effective early detection of diseases is one of the promisesof nanotechnology. Current imaging methods, such as x-rays andmagnetic resonance imaging, are limited in the size of tumors theycan detect, the depth they can penetrate the body, and by theirpotential side effects. Another promising imaging technique, nearinfrared bioimaging, is a noninvasive, painless, and non-ionizingform of radiation that operates at wavelengths just above that ofvisible light. By combining NIR imaging with nanoparticlescontaining a NIR fluorescing dye, indocyanine green, theresearchers were able to detect 5mm diameter breast cancer tumorsin a live mouse model over a period of four or more days.
Indocyanine green is the only NIR organic dye approved by the Foodand Drug Administration (FDA) for use in the human body. Thenanoparticles, which are around 20 nm in diameter—one fivethousandth the diameter of a human hair—are made of calciumphosphate, a biocompatible material that has long been used as abone replacement. Unlike other nanoparticles considered for imagingand drug delivery, e.g., semiconductor quantum dots, thebiodegradable components of calcium phosphate nanoparticles arealready widely present in the bloodstream.
In addition to the combination of near infrared imaging andnanoparticles, a second innovation is the development of afundamentally new method for processing nanoparticulates. Theprocess is called van der Waals HPLC, which stands for highperformance liquid chromatography. Materials scientist Jim Adair,whose team synthesized the particles, says “Our techniquetakes advantage of the large van der Waals forces associated withparticles, as opposed to the small van der Waals forces associatedwith molecules, atoms, and ions. The hard part in the synthesis wasmaking sure the particles did not clump together. The criticalstage was the laundering of all the nonessential byproductsassociated with the synthesis. By the end, we had a very cleansuspension of particles in which all the spectator ions, molecules,and atoms had been washed away from the basic nanoparticles.”
The Hershey group, led by pharmacologist Mark Kester, showed thattheir nanoparticles provide the fluorescent dye with 200% greaterphotoefficiency compared to indocynine green injected into thebloodstream, with a 500% greater photostability. In a separateexperiment discussed in the paper, the researchers were able toimage through 3cm of dense pig muscle tissue, which shouldcorrelate to at least 10 cm, and likely much deeper, in patients,according to Adair.
Support for this research was provided by the Penn State MaterialsResearch Institute and Penn State Hershey Medical Center, PennState College of Medicine. Partial support was also provided byKeystone Nano, Inc. Contributing to the ACS Nano article were ErhanI. Altinoglu, graduate student in materials science andengineering; Timothy J. Russin, graduate student in physics; JamesM. Kaiser, graduate student in pharmacology at Penn State Collegeof Medicine; Brian M. Barth, a research associate in the Kestergroup; Peter Eklund, Distinguished Professor of Physics andMaterials Science and Engineering; Mark Kester, G. ThomasPassananti Professor of Pharmacology; and Jim Adair, professor ofmaterials science and engineering.